Facebook recently implemented a system where you can be added to groups without any choice in the matter.  Result: technology blogger Michael Arrington, Facebook CEO Mark Zuckerberg, and Mahalo founder Jason Calacanis all found themselves added to a group called North American Man/Boy Love Association (NAMBLA). 

Adding Zuckerberg without his permission would seem to make the point privacy groups are concerned about rather clear, but it didn't.  
Facebook's groups Help Center confirms that there's simply no way to prevent people from adding you to groups. And the critics say that rather than being added automatically, friends should be given the choice to opt into any groups.
Only friends can add people to groups, which means there will be a whole lot of paring down of friend lists, making the value of Facebook much less - I will accept anyone right now because I can always hide their updates but that is not practical now.    How did Zuckerberg get added into the NAMBLA group?  Arrington wasn't too happy about it so he added him, as he is on Zuckerberg's small friend list.

This is a baffling move on the Facebook, with no definable benefit - clearly their business development people would have made a case for how this helps users if there were actually a case.  But none is forthcoming.  Instead, a new feature is foisted off on people and they have no control over it (other than making sure their email settings say you have to get an email if someone adds you - then you can quit again) and that would seem to be a likability drop for Facebook.